1. Field of the Invention
The present invention relates to spectrophotometry instruments, i.e., instruments which are able to analyze the spectral characteristics of samples.
2. Description of Related Art
An analytical instrument may be constructed in which the principal components are: a wide band radiation source (e.g., a hot filament), a sample cell, an optical filter with a defined center wavelength and bandwidth and a radiation detector. If the optical filter is chosen to match the absorption characteristics of the intended sample then the detector output will be very sensitive to the sample concentrations. An example would be an instrument that measures carbon dioxide concentrations through its strong absorption near 4.3 xcexcm.
Known drawbacks to this technique are as follows:
(a) Sensitivity will vary with inevitable changes in the components or obscuration of any of the optical elements,
(b) Absorption bands of different gaseous species often overlap so careful wavelength selection is required and limitations will exist inherent in filter technology,
(c) Temperature and pressure changes will necessitate recalculations or recalibrations.
Numerous methods are used to overcome these drawbacks, including the use of multiple detectors and wavelengths and the creation of a reference channel. However, these may not be sufficient for all applications and the cost and complexity may become unacceptable. A generally improved instrument would almost certainly use a multiplicity of detectors and filters to gather information over a wide spectral range; this range would include the full absorption band of the designated gas itself as well as those of interfering species and reference wavelengths that are not subject to attenuation.
One instrument variant that achieves some of the aims described above uses a so-called xe2x80x9cgradedxe2x80x9d or xe2x80x9cvariablexe2x80x9d filter in which the transmission characteristics vary along a defined physical dimension. This filter will be closely overlaid on a detector array so as to give wavelength discrimination along the length of the array. The remaining components of a complete analytical instrument will be as described above.
The present invention aims to provide an even more versatile radiation sensor.
In one aspect the present invention provides a radiation sensor comprising an array of detectors of electromagnetic radiation, and first and second filters positioned in front of the array whereby to limit the wavelength response of the detectors, each filter having a transmission characteristic which varies along a physical dimension, said filters being positioned such that their said dimensions are inclined with respect to each other.
As a result of the inclination or offset of the filters, the individual detectors of the array will be screened by different filter combinations such that a range of center wavelengths at a range of bandwidths can be viewed by the array.
Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings as described herein.